Despite the decrease in the incidence of early-onset group B streptococcal (GBS) disease due to widespread use of antibiotic prophylaxis during labor, GBS remains a leading cause of neonatal sepsis. Clinical features of early-onset GBS disease are similar to those of endotoxic shock, and respiratory distress is a prominent symptom. Respiratory distress may occur in newborns without a known GBS infection. Studies on the effect of GBS on pulmonary hemodynamics in animal models showed that infusion of live or heat-killed GBS into sheep promptly induced pulmonary hypertension. Curtis and associates purified and identified phospholipids (cardiolipin and phosphatidylglycerol) from the GBS cell wall as pulmonary hypertensive compounds; infusion of either cardiolipin or phosphatidylglycerol into neonatal lambs caused pulmonary hypertension. Others have demonstrated that exposure of Streptococcus mutans to penicillin induces a 15-fold increase in phospholipid release from the organism. Penicillin is one of the beta-lactam antibiotics which inhibit the normal assembly of peptidoglycan of the bacterial cell wall. These findings raised the question whether exposure of GBS to penicillin or to other beta-lactam antibiotics in newborns and mothers induces a release of GBS phospholipids causing pulmonary hypertension respiratory distress in newborns. The current recommendation is that newborns infected with GBS or whose mothers carry GBS be treated with penicillin or its derivatives. Analysis of a data file of the NICHD multicenter GBS study found a possible association between GBS colonization, penicillin treatment and respiratory distress in neonates. The results of analyses showed that 8.8% of GBS colonized newborns who did not develop early-onset GBS disease had respiratory distress within 48 h after birth compared to 1-3% of non-colonized newborns. Furthermore, colonized newborns of penicillin treated mothers were 2.6 times more likely to develop respiratory distress than those of GBS carrying but untreated mothers (95%CI:1.8-3.8). Although the effect of cardiolipin on pulmonary hypertension and of penicillin on phospholipid release from S. mutans support the role of GBS colonization and penicillin on respiratory distress in newborns, a proof of these associations requires assay of GBS phospholipids in serum samples of newborns with and without respiratory distress born of GBS-colonized mothers, treated or untreated with penicillin or other beta-lactam antibiotics during labor. A prospective study aimed at relating serum GBS phospholipid levels to the occurrence of respiratory distress in newborns of GBS colonized mothers has been completed in two U.S. academic centers: Baylor College of Medicine, Houston, Texas and Childrens Hospital and Research Center Oakland, California. Vaginal and rectal swabs were obtained during labor for GBS culture from mothers of at least 32 week gestation. A semiquantitative culture was used to determine the degree of colonization in the mothers. Demographic and clinical data were obtained from medical records. The epidemiology of GBS colonization in the study population has been described in the reference below. For cardiolipin assay, maternal and cord serum samples were collected from 3 groups of GBS colonized mothers: untreated, beta-lactam antibiotic-treated, and treated with non-beta-lactam antibiotics. All newborns were monitored for signs of respiratory distress. Two groups of newborns were assembled: with and without respiratory distress, their serum samples collected, bar-coded and stored for cardiolipin assay. An assay to quantify cardiolipin in serum has been developed in Dr. Peter Backlunds laboratory (previously directed by Dr. Alfred Yergey) using HPLC-electrospray ionization mass spectrometry. This method has been used to determine the level of endogenous tetra-linoleoyl cardiolipin in normal adult serum. This assay has been refined to determine cardiolipin levels in 200 mcL of serum. Maternal and cord-blood serum samples of colonized and non-colonized mothers and serum samples from mothers and their new borns with transient tachypnea are being assayed. These levels will be related to GBS colonization, penicillin prophylaxis and neonatal respiratory distress.